[Bug runtime/30408] Always fail to read userland memory (read faults) inside perf event probes with 6.2/6.1 kernels

[agentzh at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30408

--- Comment #4 from agentzh <agentzh at gmail dot com> ---
OK, I tracked it down to be the user_addr_max() macro missing since 5.18, which
is in the stap runtime's lookup_bad_addr_user() function. In perf event probe
handlers, the in_task() macro always returns 0 (false). in_task() is a macro
defined as

```
#define in_task()  (!(in_nmi() | in_hardirq() | in_serving_softirq()))
```

And the kernels use hardirq contexts for perf events like
`perf.type(1).config(0).sample(100000)`, and thus in_hardirq() returning 1.

For comparison, the kernel's own bpf_probe_read_user() function does not check
in_task(), in_hardirq(), or user_addr_max() (though it has another deadlock
regression since 5.19 on the code path copy_from_user_nofault ->
check_object_size -> find_vmap_area() around the vmap_area_lock lock, but that
is another story).

The following patch seems to fix this for me:

https://gist.github.com/agentzh/948f77381c1f1e2cb7474c22c2c17c0e

So this regression really appeared since 5.18.

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